DVB-T dongles based on the Realtek RTL2832U can be used as a cheap SDR, since the chip allows transferring the raw I/Q samples to the host, which is officially used for DAB/DAB+/FM demodulation. The possibility of this has been discovered by Eric Fry (History and Discovery of RTLSDR). Antti Palosaari has not been involved in development of rtl-sdr.

The RTL2832U outputs 8-bit I/Q-samples, and the highest theoretically possible sample-rate is 3.2 MS/s, however, the highest sample-rate without lost samples that has been tested so far is 2.56 MS/s. The frequency range is highly dependent of the used tuner, dongles that use the Elonics E4000 offer the widest possible range (see table below).

Tuner

Frequency range

Elonics E4000

52 - 2200 MHz with a gap from 1100 MHz to 1250 MHz (varies)

Rafael Micro R820T

24 - 1766 MHz

Rafael Micro R828D

24 - 1766 MHz

Fitipower FC0013

22 - 1100 MHz (FC0013B/C, FC0013G has a separate L-band input, which is unconnected on most sticks)

Note: Many devices with EEPROM have 0x2838 as PID and RTL2838 as product name, but in fact all of them have an RTL2832U inside.brRealtek never released a chip marked as RTL2838 so far.The following devices are known to work fine with RTLSDR software:

Much software is available for the RTL2832. Most of the user-level packages rely on the librtlsdr library which comes as part of the rtl-sdr codebase. This codebase contains both the library itself and also a number of command line tools such as rtl_test, rtl_sdr, rtl_tcp, and rtl_fm. These command line tools use the library to test for the existence of RTL2832 devices and to perform basic data transfer functions to and from the device.

Because most of the RTL2832 devices are connected using USB, the librtlsdr library depends on the libusb library to communicate with the device.

At the user level, there are several options for interacting with the hardware. The rtl-sdr codebase contains a basic FM receiver program that operates from the command line. The rtl_fm program is a command line tool that can initialize the RTL2832, tune to a given frequency, and output the received audio to a file or pipe the output to command line audio players such as the alsa aplay or the sox play commands. There is also the rtl_sdr program that will output the raw I-Q data to a file for more basic analysis.

For example, the following command will do reception of commercial wide-band FM signals:

If you want to do more advanced experiments, the GNU Radio collection of tools can be used to build custom radio devices. GNU Radio can be used both from a GUI perspective in which you can drag-and-drop radio components to build a radio and also programmatically where software programs written in C or Python are created that directly reference the internal GNU Radio functions.

The use of GNU Radio is attractive because of the large number of pre-built functions that can easily be connected together. However, be aware that this is a large body of software with dependencies on many libraries. Thankfully there is a simple script that will perform the installation but still, the time required can be on the order of hours. When starting out, it might be good to try the command line programs that come with the rtl-sdr package first and then install the GNU Radio system later.

The Gnu Radio source requires a recent gnuradio (>= v3.7 if building master branch or 3.6.5 when building gr3.6 branch) to be installed.

The source supports direct device operation as well as a tcp client mode when using the rtl_tcp utility as a spectrum server.

Please note: prior pulling a new version from git and compiling it, please do a "make uninstall" first to properly remove the previous version.

Please note: you always should build & install the latest version of the dependencies (librtlsdr in this case) before trying to build the gr source. The build system of gr-osmosdr will recognize them and enable specific source/sink components thereafter.

If you are building for gnuradio 3.6 series, you have to switch to the gr3.6 branch as follows

git checkout gr3.6

then continue with

mkdir build
cd build/
cmake ../

Now cmake should print out a summary of enabled/disabled components. You may disable certain components by following guidelines shown by cmake. Make sure the device of your interest is listed here. Check your dependencies and retry otherwise.

use the rtl_tcp=... device argument in gr-osmosdr source to receive the samples in GRC and control the rtl settings remotely.

This application has been successfully crosscompiled for ARM and MIPS devices and is providing IQ data in a networked ADS-B setup at a rate of 2.4MSps. The gr-osmosdr source is being used together with an optimized gr-air-modes version (see Known Apps below).It is also available as a package in OpenWRT.

To convert the data to a standard cfile, following GNU Radio Block can be used:brThe GNU Radio Companion flowgraph (rtl2832-cfile.grc) is attached to this page. It is based on the FM demodulation flowgraph posted by Alistair Buxton on this thread.

Please note: for realtime operation you may use fifos (mkfifo) to forward the iq data from the capture utility to the GRC flowgraph.

You may use any of the the following gnuradio sources (they are equivalent):brbr!osmosource.png[[br]]